Metro's five-month experiment with automatic teller machines at six stations has been such a success that the regional transit agency probably will make the machines permanent and install them at more stations, officials say.

In May, teller machines were installed at the Farragut West and Foggy Bottom stations in the District, the Silver Spring and New Carrollton stations in Maryland and the Pentagon and Vienna stations in Virginia. Depending on which bank card they have, riders can buy farecards, withdraw cash or both.

Through August, the last month for which figures are available, the machines averaged between 30,000 and 35,000 transactions a month, or between 4,000 and 7,000 transactions for each machine. That translates to about $80,000 in sales of farecards a month.

"From Metro's point of view, at the present time there is no obvious problem with this," said Peter Benjamin, Metro's planning director. "It's a win-win situation. It costs us less money, is a convenience to our customers and is useful to the banks too."

Sovran Bank, which installed the machines and maintains them, also is pleased with the experiment. Although bank officials said they will take a look at the experiment after 10 months, "we're thrilled so far and feel like it will continue," said Nancy Poe, director of Sovran's CashFlow program.

Riders with CashFlow and Most cards can use the machines to get cash and buy farecards with a value of $10 or $20 that include a 5 percent bonus. This encourages people to buy higher value farecards.

Holders of Visa, Plus, Relay, Armed Forces Financial Network and some MasterCards can withdraw cash but cannot buy farecards. The service is free for Sovran customers; other bank customers may be charged 50 cents for farecards, but won't be charged by Sovran for withdrawing money. Their banks may charge them, however, for using a Sovran teller machine.

If the experiment is made permanent, Sovran will pay Metro a fee for each transaction. Although the amount of revenue has not been estimated, Metro officials believe the greater benefit is to the system's riders, who make a half-million trips a day on the trains. Metro also gains, in effect, a new farecard machine without having to pay for it, maintain it or count the money, Benjamin said.

Figures show that the Vienna station's teller machine is the most heavily used, probably because of the long ride and higher fare. Foggy Bottom has the largest number of cash transactions, Benjamin said, in part because of George Washington University students "who are using the machine to get money before a date."